MONDAY, Nov. 26 (HealthDay News) -- Doctors should let their teenage patients know about emergency contraception, such as Plan B, and write them a prescription for it if they are sexually active, according to a new policy statement from the American Academy of Pediatrics.

The new guideline is an update to the 2005 policy statement from the American Academy of Pediatrics (AAP), the largest organization of pediatric doctors in the United States.

Since 2005, "the data are even more supportive of emergency contraception," said the policy statement's lead author, Dr. Cora Breuner, A professor of pediatrics and adolescent medicine at the University of Washington in Seattle.

"These methods are absolutely not an abortion," Breuner said. They prevent pregnancies by blocking fertilization.

The statement, published online Nov. 26 in the journal Pediatrics, emphasizes the importance of informing teens that emergency contraception is available if they have unprotected sex or if their protection fails, and that it is most effective if taken within one day of having unprotected sex.

Emergency contraception is available without a prescription for girls 17 and older and boys 18 and older, but younger teens need a prescription in most states. Having a prescription ready to go can make it more likely that teens will use emergency contraception, Breuner said.

The target patient group for this policy statement is women 15 to 25 years of age, but even some women in their 30s and 40s should know more about emergency contraception as a back-up option to prevent pregnancies, Breuner said.

Although teen birth rates have decreased since the 1990s, the United States still has one of the highest rates among developed countries. And more than three-quarters of teen pregnancies are unintended, according to background information in the study. About 34 out of every 1,000 women between 15 and 19 years old gave birth in 2010.

"People say that if you make this available that kids will have more sex and less protected sex, and that is not true," Breuner said. "Seven studies showed that is not true."

Roughly 42 percent of 15- to 19-year-olds report having had sex, and 10 percent of them say they were forced into it, the statement noted.

Breuner and her colleagues reviewed the safety and effectiveness of three emergency contraception methods: Plan B or Next Choice (levonorgestrel) and ella (ulipristal acetate), which affect the hormone progesterone, and combination oral contraceptives. Ella is the newest method, approved by the U.S. Food and Drug Administration in 2010.

Plan B users are about half as likely to experience nausea and vomiting as those taking ella, but the rates of side effects are fairly low for both.

Emergency contraception is most effective in the first 24 hours after unprotected sex, but can reduce the risk of pregnancy for up to 120 hours (five days). One study found that, among women taking Plan B within 72 hours of unprotected sex, 1.1 percent became pregnant.

Although emergency contraception does not generally interfere with established pregnancies, ella can cause miscarriage in the first trimester. As a result, women must have a negative pregnancy test and a prescription to receive ella, making it a less ideal choice than Plan B, Breuner said.

The third method, combination oral contraceptives, is less popular because it involves estrogen along with progestin and is associated with higher rates of minor side effects.

Many pediatricians do not know enough about how emergency contraception works to discuss it with their patients, Breuner said. Some doctors won't prescribe it because of biases but they should refer patients to someone who will, she added.

Dr. Jennifer Reed, associate professor of pediatrics at Cincinnati Children's Hospital Medical Center, said many doctors only see teens when they are sick or injured, and they should take that opportunity to bring up subjects like emergency contraception and sexually transmitted diseases.

"I think [the policy statement] will bring awareness to pediatricians and hopefully give guidance to what is accepted," said Reed, who was not involved in writing the statement.

School nurses and health clinics also can play an important role in educating teens about emergency contraception, Breuner said.

Studies have found that as few as half of teens know about emergency contraception, and among those who are aware, only half know the correct timing for taking it, according to the policy statement.

"If we are going to do anything about reducing our teen pregnancy rate and make it not the highest in the developed world, we need to provide more education to family and children," Breuner said.

Although there are no studies showing that improving access to emergency contraception reduces pregnancies in the general population, Breuner thinks this is because not enough women have been using it to see a difference.